1. Field of the Invention
The present invention relates to a method and apparatus for removing toxic gas components exhausted from a semiconductor process using same.
2. Description of the Related Art
In the manufacture of semiconductors, the toxic, flammable, and corrosive nature of hydride and acid gases pose considerable health and environmental hazards in addition to jeopardizing the integrity of exhaust systems.
Material gases, such as BF3, AsH3 and PH3 are used as primary dopant gases in ion implantation processes. Other gases, such as SiF4, GeF4, (hfac)In(CH3)2 and Br2Sb(CH3) etc. are also used.
In the case of MOVPE/PECVD gases such as SiH4, SiF4, NH3, AsH3 and PH3 are delivered to a process chamber through electrically isolated assemblies. AsH3 or PH3 are flowed at particularly high rates during deposition to provide atomic As or P of GaAs or GaP, respectively. HCl can be flowed over Ga metal in order to provide GaCl as a precursor to the atomic Ga of GaN. Epitaxial dielectric is deposited from SiH4.
HCl and HF can be used for chamber cleans by creating radicals in a plasma stream, which flow to areas in the chamber where excess film accumulates. The radicals react with the deposited film to create gaseous by-products. The by-products are then removed from the chamber and pumped out as effluent.
Ongoing research focused on reducing emission levels of such toxic gases from the effluent waste streams of semiconductor manufacturing processes, involves the optimization of abatement processes. Current processes include a variety of thermal, wet and/or dry scrubbing operations.
Thermal scrubbers react an oxidizing agent (almost always air) with a target component (e.g. AsH3, PH3, etc.) in a process effluent stream to produce an oxidized species of the target component (e.g. As2O3, P205, etc.). The oxidized species is then removed from the effluent stream by contacting the stream with a gas absorption column (water scrubber). The disadvantages of such a system are (a) it is energy intensive in that it requires significant amounts of electricity and/or fuel, such as H2 or CH4, (b) it requires water, and (c) it produces an aqueous hazardous waste stream when it scrubs arsenic containing compounds.
Wet scrubbing of effluent streams involves contacting the effluent gas from a specific process with a scrubbing liquid to cause undesired effluent stream components to be absorbed by the liquid, or to react with the liquid (e.g., a caustic solution for contacting with an acid gas effluent) to effect the removal of the undesired components from the gas phase. Often the scrubbing liquid includes an oxidizing agent such as potassium permanganate, a regulated substance, or sodium hypochlorite, which leads to unwanted precipitation reactions. Further, the wet scrubbing system requires the consumption of significant amounts of the oxidizing agents and leads to a contaminated aqueous waste stream.
Dry scrubbing involves contacting the effluent gas with a solid material which functions to chemisorb or react with the undesired components to effect their removal. Dry scrubbing concentrates and fully contains hazardous abated components, is passive in operation, has no moving parts and works on demand, making it the safest and most preferable mode of abatement operation.
With respect to ion implant processes it is expected that fluorinated acid gases will pass through an ion implant system largely intact, while hydride source gases will pass through only moderately intact. Thus, the large flow-rates of intact acid gas components and the high toxicity and low levels of permissible personnel exposure of hydride gas components (for example, the threshold limit value (TLV) for AsH3 is 0.05 ppm, or a IDLH of 3 ppm) mandate highly efficient effluent stream treatment and/or abatement for removal of both gas types.
In addition to the foregoing issues incident to the use and operation of ion implantation systems, empirical characterization of ion implant process exhaust streams reveal significant emissions of hazardous gases in the process system from source gas pumps, roughing pumps and from cryogenic pump regeneration cycles.
It is important to note that for dry scrubbing purposes, the chemical requirements to scrub acid gases such as BF3 and SiF4 are entirely different than the chemical requirements to scrub hydride gases such as AsH3, PH3 and GeH4.
With respect to chemical vapor deposition (CVD) processes, an acid gas and/or hydride gas may be used in combination with large amounts of a ballast or process gas, (e.g. hydrogen). Dry scrubbing of effluent streams deriving from such a process is difficult because a secondary reaction, typically reductive hydrogenation may occur between the scrubbing material and hydrogen at a temperature around 110° C. to 120° C. The secondary reaction, once initiated, may lead to a “runaway” situation, where temperatures in the scrubbing material reach 600° C.
Cupric oxide CuO, cupric hydroxide Cu(OH)2, and copper carbonate CuCO3, based materials are used in resin scrubbing materials for abatement of hydride compounds from semiconductor effluent streams. Although most copper based resins react exothermically with hydrides, CuO and Cu(OH)2, materials can exotherm severely at temperatures between 110° C. to 120° C. in the presence of large quantities of hydrogen.
For example, U.S. Pat. Nos. 4,743,435, 4,910,001 and 4,996,030 disclose methods for removing hydride gas species from MOCVD applications using CuO based resins. However, the capacity of CuO based materials is limited due to the copper surface area and when attempts are made to increase CuO content, most notably by addition of CuO to a metal oxide mixture used to create the resin, the surface area can drop inordinately. Additionally, the material can exotherm severely due to the heats of adsorption and reaction of the hydride gas and since most CVD applications use large amounts of H2 as carrier gas with AsH3 and PH3, temperature of the CuO material is critical, as exceeding a temperature of approximately 110° C. to 120° C. may result in the reduction of the CuO material by H2, thereby creating severe exotherms that can exceed 500° C. to 600° C.
U.S. Pat. No. 5,853,678 discloses a method of removing harmful, volatile, inorganic hydrides, inorganic halides and organometallic compounds by contacting the harmful compound with crystalline cupric hydroxide. However, similar to CuO based materials, crystalline cupric hydroxide, Cu(OH)2, based materials react with hydride gases to undergo H2 reduction reactions in approximately the same temperature regime as CuO.
Japanese publication JP1996059391A discloses a method of removing Group V species from effluents containing same by contacting the Group V species with basic copper carbonate CUCO3·Cu(OH)2. Basic copper carbonate undergoes H2 reduction reactions at temperatures higher than both CuO and Cu(OH)2.
It would therefore be a significant advance in the art, and accordingly is an object of the present invention, to provide an abatement system capable of handling acid, hydride and/or metalorganic gases, which eliminates or at least ameliorates the aforementioned hazards of conventional CuO and Cu(OH)2 processes.
It is another object of the invention to provide an improved system for the treatment of effluent streams comprising acid, hydride and/or metalorganic gaseous components having a potential operating temperature regime that is greater than 100° C.
It is another object of the instant invention to provide a safe, low-cost, high capacity, high efficiency system for the treatment of effluent streams comprising acid, hydride, and/or metalorganic gaseous components.
Other objects and advantages will be more fully apparent from the ensuing disclosure and appended claims.